Pressure Phase-plane Based Determination of the Onset of Left Ventricular Relaxation
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Contraction–relaxation coupling is often characterized in terms of its effects on contraction or relaxation parameters, such as the time-constant of isovolumic relaxation (τ). While thermodynamics-based LV function characterization methods exist, landmark relaxation-onset determination studies used surgical methods. One classic, open-chest preparation study found that relaxation-onset occurs during early ejection, i.e. 34% of systolic time, T SYS, defined as the time from end-diastolic pressure to peak negative dP/dt. Because ventricular pumping is a steady state system, the laws of thermodynamics and nonlinear dynamics require that energy generation (during contraction) and energy utilization (during relaxation) must be balanced in a time-averaged (steady-state) sense. We calculated both energy generation and energy utilization, via novel pressure phase-plane (PPP) based parameters, including isovolumic stiffness analogs, in 29 subjects, 20 cardiac cycles per subject (580 beats). Results in control subjects show that relaxation-onset occurs near or prior to 34% of T SYS. In hearts with sever dysfunction including prolonged τ, relaxation-onset commences after 50% of T SYS (p < 0.05). We conclude that PPP-based analysis can characterize relaxation-onset in vivo in thermodynamic and nonlinear dynamics terms without requiring an open-chest preparation, and may facilitate characterization of cellular mechanisms of relaxation-onset at the organ system level.
KeywordsHemodynamics Diastole Relaxation Pressure phase plane Limit cycle
We thank the staff of the Cardiac Catheterization Laboratory at Barnes Jewish Hospital for assistance in data acquisition and Leonid Shmuylovich for helpful comments in manuscript preparation. Helpful comments regarding energy flux by Professor Guy Genin is gratefully acknowledged. CSC is currently at the Department of Molecular and Cellular Biology, University of Arizona, Tucson AZ. Supported in part by the American Heart Association Heartland Affiliate (0610042Z, CSC), Whitaker Foundation, National Institutes of Health (HL54179, HL04023 SJK), the Barnes-Jewish Hospital Foundation and the Alan A. and Edith L. Wolff Charitable Trust.
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